What are the health risks that a high-protein diet can pose? What should we watch out for and what should we know?

This article will be the first in a series, which will focus on protein consumption.

This one will deal with the effects of protein on health.

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A seemingly negative aspect of higher protein intake is related to bone health and the potential increase in dietary acid load from it.

The acid ash hypothesis posits that increased protein intake (specifically sulphur-containing amino acids) leads to a greater dietary acid load, which is regulated through the release of bone-derived alkalinizing compounds, resulting in bone resorption, osteoporosis and hypercalciuria.

However, in this investigation, bone density was not correlated with the ratio of animal to vegetable protein intake, despite the fact that animal protein provides acid precursors, while vegetables provide base precursors not found in animal foods.

Even worse, the so-called acid ash hypothesis has been subjected to meta-analysis and found to lack support.

A meta-analysis in 2009 found that, contrary to the acid ash hypothesis, higher phosphate intake is associated with reduced urinary calcium and increased calcium retention.

At this analysis using the Bradford/Hill criteria to prove causality, it was clear that the association between dietary acid load and osteoporotic bone disease was not supported by evidence, while in one recent analysis conducted by the US National Osteoporosis Foundation, the authors concluded that in a high-protein diet there are positive rather than negative trends in bone density in most bone regions. In agreement with this conclusion, it has been suggested that protein in the diet supports bone health, but this probably only happens when calcium intake is adequate.

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In a 6 months intervention In women with exercise experience, comparing the effects of a high-protein diet (2.8g/kg per day) versus a control group (1.5g/kg per day), the researchers found no differences in bone density, while in a weight loss program with diet and exercise that lasted 16 weeks, consumption of dairy foods and higher protein, combined with adequate intake of calcium and vitamin D resulted in improved indicators of bone health and calcium metabolism in overweight and obese young women.

Besides, as has been pointed out, the correlation between changes in calcium excretion and changes in urinary acid excretion is not evidence that the source of the excreted calcium is from bone or that this calcium in urine contributes to the development of osteoporosis.

In fact, data from calcium isotope studies suggest that the main source for the increase in urinary calcium from a high-protein diet comes from increased absorption of dietary calcium and not from bone resorption.

Therefore, in general, it seems that not only does protein not damage bones, but is an essential nutrient for their health. Her recruitment seems to have positive effect on calcium balance and thus on the maintenance of bone density.

Since exercise provides a stimulus for protein growth in skeletal muscle, it is not uncommon to recommend intake levels ranging from 1.4g/kg to 2.0g/kg per day during prepubertal development, so that this stimulus can be converted into additional muscle tissue, which is in turn an important predictor of concentration bone mass during this period.

In addition, there is a lack of scientific evidence linking higher intakes of dietary protein to negative outcomes in healthy people who exercise, while certain elements suggest that older men and women (the segment of the population most susceptible to osteoporosis) should consume protein above current recommendations (0.8g/kg per day) to optimise bone mass.

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The relationship between high protein intake and type 2 diabetes is still under debate and results vary depending on the duration of the study, the protein source and whether there was weight gain. The most important factor of concern linking protein to diabetes is amino acids.

Circulating levels of branched-chain amino acids (BCAAs) are excellent biomarkers of metabolic health and their elevated blood levels are insulin resistance markers and consequently type 2 diabetes.

Recent research has shown, however, that the causality is reversed, as not only the data do not support their role as causal agents, but even that the increased concentrations of amino acids in the blood come from their defective catabolism compared to healthy individuals, which is also supported by genetic studies.

So, we can say that when high protein diets with high protein intake and calorie control are applied with the aim of losing or maintaining weight, usually we can expect favourable results in relation to insulin sensitivity.

On the other hand, a diet that increases body fat will always have negative effects on metabolic health.

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A common reason why higher protein intake is not recommended for older people is the risk of kidney disease.

However, analyses show that this has no basis in fact.

There is general agreement on the effect of dietary protein restriction on the slowing the reduction in glomerular filtration rate (GFR) among most forms of kidney damage to man.

Although there are possible pathways that have been suggested through which a higher protein diet could facilitate kidney damage, the magnitude of the effect and whether it actually exists remains unknown.

The idea that protein restriction may delay the deterioration of kidney function associated with ageing was based on in studies in rats in which low-calorie or low-protein diets slow the development of chronic kidney failure.

But, deterioration of kidney function occurs completely differently in rats, which means that this mechanism is unlikely to work in humans.

Also, when creatinine clearance was measured in humans at intervals of 10 to 18 years, the deterioration was not associated with protein intake.

In fact, the correlation of creatinine clearance with protein intake shows a relationship with a positive slope, suggesting that low protein intake itself reduces kidney function.

This meta-analysis showed that glomerular filtration rate (GFR), as an indicator of renal function, does not decrease when people have a higher protein intake, but rather increasesalthough this meta-analysis in people with normal kidney function, suggests that the effect may be insignificant or even nonexistent, even in populations at higher risk of reduced kidney function, such as people with type 2 diabetes.

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It is believed that this overfiltration of the kidneys is the result of nephron damage. However, in humans, glomerular hyperfiltration occurs at the level of the whole kidney as a result of increased blood flow in the kidneys.

It is important to understand that the ability of the kidney to increase GFR under certain stimuli or demands is a normal response to increased solute load size and does not represent a risk factor for the development of chronic kidney disease. In addition, pregnancy and unilateral nephrectomy are characterized by significant renal hypertrophy and hyperfiltration with increases in GFR, while the kidney function remains physiological.

These factors lead to the conclusion that dietary protein content is not responsible for the gradual decline in renal function over time, but rather that this decrease in glomerular filtration rate is a natural consequence of a decrease in protein intake as we age.

In the most recent round of discussions on the determination of Arbitral Recruitment Reference, the US Institute of Medicine concluded that the protein content of the diet is not responsible for the gradual decline in kidney function over time, with the report of the World Health Organization and the International Food and Agriculture Organization to reach the same conclusion.

This raises the question of whether and how and over what period of time these high protein intakes can adversely affect health.

Recent studies with medium-term interventions and high protein content in caloric balance or surplus reported no adverse effects.

In one of the longest-running dietary intervention trials, which lasted 2 years, comparing higher to lower protein intakes, it was reported that in otherwise healthy obese individuals, a low-carbohydrate but high-protein weight loss diet was not associated with harmful effects on GFR or proteinuria.

This study on men who did weight training, lasted one year. Subjects were switched between their usual diet (which was already high in protein) and a higher protein diet. So, on average, each person consumed their usual diet for 6 months and a higher protein diet for 6 months. Throughout the year, they consumed 2.51-3.32g/kg of protein per day. However, there were no detrimental effects on blood lipid measurements, as well as liver and kidney function, despite the overall increase in energy intake during the high-protein phase.

Similarly, overweight and obese volunteers with pre-diabetes on a higher protein diet had a significant increase in urea and urinary urea/creatinine ratio after one year. However, there were no correlations between increased protein intake and creatinine clearance, estimated glomerular filtration rate, urinary albumin/creatinine ratio or blood creatinine. Thus, after 1 year of higher protein intake in pre-diabetic older adults, no evidence of impaired kidney function was found.

In addition, this investigation showed that in a weight loss diet, both a medium and a higher protein diet lead to normalised renal function over the 12-month period in people with type 2 diabetes and early kidney disease.

Bones, Bones, Bones, Bones, Bones, Bones, Bones, Health, Protein, Health, Diabetes, Kidney, Kidney, Kidneys

However, the limits of adaptation to a long-term high-protein diet need to be explored.

Although it appears that dietary protein intakes above the Dietary Reference Intakes are not harmful to the healthy exercising population, people vulnerable to kidney disease (such as nephrolithiasis) or with mild renal impairment should monitor their protein intake closely, as epidemiological studies provide evidence that protein intake may be associated with the development of kidney disease, as in studies such as this one, where only patients with pre-existing dysfunction appeared to have an increased risk of developing kidney stones and kidney disease.

The truth is that more research needs to be conducted in adults and the elderly in relation to exercise, skeletal muscle hypertrophy and protein intake and their cumulative effects on health in general.

But it is also true that chronic total protein and amino acid intake below the daily requirements is detrimental to bodily functions, leading to higher risk for disease and mortality .

Overall, the implementation of a high-protein diet does not seem to have adverse effects on already healthy individuals. Although there is no clear recommendation defining a safe upper limit of protein intake, consumption of up to 40% calories of protein per day has not been associated with increased risks on health in otherwise healthy people.

-Suprastratum: The authority on health, fitness and nutrition

Sources/bibliography/more reading:

Protein and bone health:

Protein and type II diabetes:

Protein and kidney health:


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Author: Nick Krontiris

Founder, Suprastratum


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